Data storage system with complex memory and method of operating the same

ABSTRACT

A data storage system and a data storing method for the data storage system are provided. The data storage system includes a host unit, a storage unit, and a first input/output bus functioning as an interface between the host unit and the storage unit. The storage unit includes a non-volatile memory buffer unit and a flash memory unit. The non-volatile memory buffer unit includes a plurality of buffers arranged in parallel. The flash memory unit includes a plurality of data storage devices arranged in parallel to input and output data using a parallel method. In the method, a writing request is first classified into one of a plurality of grades according to a writing request frequency when there is a writing request and the writing requested data is stored in one of the non-volatile memory buffer unit and the flash memory unit according to the writing request frequency.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2005-0063301, filed on Jul. 13, 2005, and Korean Patent Application No. 10-2005-0076368, filed on Aug. 19, 2005 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a data storage system and method of operating the same, and more particularly, to a data storage system with a complex memory comprising a flash memory and a method of operating the data storage system.

2. Description of the Related Art

Data storage systems using a flash memory device have been widely used in an embedded system and a mobile system. The data storage system using a flash memory device is one of electrically erasable programmable read-only memories (EEPROMs) on and from which the data can be written, read, and erased. While reading speed of the data storage system using a flash memory device is fast, writing and erasing speeds thereof are slow.

In the data storage system using a flash memory device, the data input/output unit is a page of 2-Bytes or 4-Bytes for a NOR-type flash memory device and 512-Bytes or 2-Kbytes for a NAND-type flash memory device. In addition, the erasing operation unit is a block of 128-Kbytes for the NOR-type flash memory device and 16-Kbytes or 64-Kbytes for the NAND-type flash memory device.

That is, for the NOR-type flash memory device, it takes about 400 μs to write 2-Bytes. For the NAN D-type flash memory device, it takes about 220 μs to write 512-Bytes and takes about 2 ms-2 s to erase 512-Bytes. That is, for the NAND-type memory device, the erasing operation is relatively slow.

In contrast, for a random access memory (RAM) device, it takes several tens of nano seconds to store a word. That is, the writing speed of data storage systems using the flash memory device is far slower than that of the RAM device.

Accordingly, a flash memory device is generally used as a code memory device that does not frequently undergo writing operations or an auxiliary memory device of which writing performance is not important. In addition, a data storage system using a flash memory device cannot perform real-time data storing operation. Thus, there are limitations in using the data storage systems using a flash memory device in a digital product such as a digital camera or a digital camcorder.

Therefore, a technology for logically and effectively hiding the erasing operation using a flash translation layer (FTL) employed using hardware or software has been developed (refer to U.S. Pat. No. 6,311,290 to J. Kim, et al. and “A space-Efficient Flash Translation Layer for Compact Flash systems” IEEE Trans. Consumer Elec., Vol. 48, No. 2 pp, 366-375, 2002).

However, even when the erasing operation is hidden using the FTL, the writing speed of flash memory devices are still slow compared to RAM devices. Thus, in the case of storing mass data, the writing speed of a data storage system using a flash memory is less than that of a RAM device. Due to this, a flash memory device is generally used as a code memory device that does not frequently undergo writing operations or as an auxiliary memory device of which writing performance is not important. Particularly, flash memory devices are very limited in being used in a device such as the digital camera, camcorder and mobile phone that process and store data in real-time.

An input/output buffer (or cash) is used to improve the input/output performance of the flash memory device. Korean Patent Application No. 2003-32552 discloses a data storage system that uses an SRAM or DRAM as the input/output buffer (or cash). U.S. patent application Ser. No. 2004/0193782 A1 discloses a data storage system that improves writing performance by using a magnetic RAM as a writing buffer.

In the data storage system disclosed in Korean Patent Application No. 2003-32552, input performance can be improved by maintaining data that is frequently accessed in the cash, which has a fast input/output speed, using a temporal-spatial locality appearing in an input/output pattern of the flash memory device. However, when the writing operation is done only in the cash, the data may be erased if power is turned off before the data is stored in the flash memory device. That is, the data maintenance that is a basic condition of the data storage system cannot be ensured. Therefore, although the reading performance is improved, the an ideal writing performance is not yet satisfied.

In the data storage system disclosed in U.S. patent application Ser. No. 2004/0193782 A1, when a writing operation larger than the capacity of a MRAM used in the system is continuously requested, an overflow is generated in the MRAM and thus the following writing request is directly done in the flash memory device. This leads to a deterioration of the writing performance.

SUMMARY OF THE INVENTION

The present invention provides a data storage system with a complex memory that has an increased writing speed realized by managing only data which will be frequently updated in a writing buffer taking advantage of spatial locality and can reduce the number of writing and erasing operations for the flash memory that is an advantage obtained by using the buffer while reducing the size of the buffer.

The present invention also provides a method of operating the data storage system.

According to an aspect of the present invention, there is provided a data storage system including: a host unit; a storage unit; and a first input/output bus functioning as an interface between the host unit and the storage unit, wherein the storage unit includes a non-volatile memory buffer unit and a flash memory unit, the non-volatile memory unit including a plurality of buffers arranged in parallel, and the flash memory unit including a plurality of data storage devices arranged in parallel to input and output data using a parallel method.

The number of buffers included in the non-volatile memory buffer unit may be greater than the number of data storage devices included in the flash memory unit.

Each buffer may be a bank having a predetermined data storage capacity.

Each buffer may be a non-volatile memory chip.

Each data storage device may be a bank, and each bank may include a plurality of pages each having a predetermined data storage capacity.

Each data storage device may be a flash memory chip.

A data storage capacity of each buffer may be equal to, or N (N=1, 2, 3) times, that of each page.

A data storage capacity of each buffer may be equal to, or N (N=1, 2, 3) times, a block size that is a deleting unit of the flash memory.

According to another aspect of the present invention, there is provided a method of writing data in a data storage system including a host unit, a storage unit and a first input/output bus functioning as an interface between the host unit and the storage unit, wherein the storage unit includes a non-volatile memory buffer unit and a flash memory unit, the non-volatile memory unit includes a plurality of buffers arranged in parallel and the flash memory unit including a plurality of data storage devices arranged in parallel, the method including: writing data in a first buffer of the plurality of buffers; writing data in a second buffer of the plurality of buffers; writing data in a third buffer of the plurality of the buffers; writing the data written in the first buffer in a first page of a first data storage device of the plurality of data storage devices; and writing the data written in the second buffer in a first page of a second data storage device of the plurality of the data storage devices, wherein the writing of the data in the second buffer and the writing of the data written in the first buffer in the first page are simultaneously performed and the writing of the data in the third buffer and the writing of the data written in the second buffer in the first page are simultaneously performed.

The method may further comprise writing the data written in the third buffer in a second page of the first data storage device of the plurality of data storage devices, wherein new data are written in the first buffer during the writing of the data written in the third buffer in a second page of the first data storage device of the plurality of data storage devices. The method may further comprise deleting the data written in the first buffer before the new data is written in the first buffer.

The number of buffers included in the non-volatile memory unit may be greater than the number of data storage devices included in the flash memory unit. Each buffer may be a bank having a predetermined storage capacity.

According to still another aspect of the present invention, there is provided a method of writing data in a data storage system including a host unit, a storage unit and a first input/output bus functioning as an interface between the host unit and the storage unit, wherein the storage unit includes a non-volatile memory buffer unit and a flash memory unit, the non-volatile memory unit including a plurality of buffers arranged in parallel, and the flash memory unit including a plurality of data storage devices arranged in parallel, the method including: writing data written in a first page of a first data storage device of the plurality of data storage devices in a first buffer of the plurality of buffers; writing data written in a first page of a second data storage device of the plurality of data storage devices in a second buffer of the plurality of buffers; writing data written in a second page of the first data storage device of the plurality of data storage devices in a third buffer of the plurality of buffers; wherein the writing of the data written in the first page of the second data storage device starts after the writing of the data written in the first page of the first data storage starts and ends after the writing of the data written in the first page of the first data storage device ends and the writing of the data written in the second page of the first storage device starts after the writing of the data written in the first page of the first data storage device ends; and while the writing of the data written in the first page of the second data storage device in the second buffer is performed, the data written in the first buffer is read and while the writing of the data written in the second page of the first data storage device in the third buffer is performed, the data written in the second buffer is read.

The method may further include writing data written in a second page of a second data storage device in the first buffer after the data written in the first buffer is read and before the writing of the data written in the second page of the first data storage device in the third buffer ends.

According to still yet another aspect of the present invention, there is provided a method of storing data in a data storage system having a flash memory unit and a writing buffer unit, the method including: classifying a writing request into one of a plurality of grades according to a writing request frequency when a writing request is made; and storing the writing requested data in one of the memory unit and the writing buffer unit according to the writing request frequency.

In the method, the storing of the writing requested data may comprise storing a page having a relatively high writing request frequency in the writing buffer unit, and, when the writing buffer unit is full, storing one of the pages stored in the writing buffer unit in the flash memory unit.

When the writing request is classified into one of two grades, the data having a relatively high writing request frequency may be stored in the writing buffer unit and the data having a relatively low writing request frequency are stored in the flash memory unit.

Alternatively, when the writing request is classified into one of two grades, the storing of the writing requested data may include: temporarily storing data having a relatively high writing request frequency in a first writing buffer of the plurality of writing buffers; temporarily storing data having a relatively low writing request frequency in a second writing buffer of the plurality of writing buffers or the the flash memory unit.

Alternatively, when the writing request is classified into one of three grades, the storing of the writing requested data may include: temporarily storing data having a relatively high writing request frequency in a first writing buffer of the plurality of writing buffers; temporarily storing data having a middle writing request frequency in a second writing buffer of the plurality of writing buffers; and storing data having a relatively low writing request frequency in the flash memory unit.

Alternatively, when the writing request is classified into one of three grades, the storing of the writing requested data includes: temporarily storing data having a relatively high writing request frequency in a first writing buffer of the plurality of writing buffers; temporarily storing data having a middle writing request frequency in a second writing buffer of the plurality of writing buffers; and temporarily storing data having a relatively low writing request frequency in a third writing buffer of the plurality of writing buffers.

When there is a page for the writing request available in the writing buffer unit, the page of the writing buffer unit may be updated to the available page in the writing buffer unit regardless of the classification of the writing request.

The classifying of the writing request may include classifying the writing request as a hot or cold pages using one or more LRU (Least Recently Used) Q.

Alternatively, the classifying of the writing request may include adding a count value to the writing request and classifying the writing request according to whether the count value is reduced to a predetermined value after a predetermined time has lapsed.

When the data having the relatively high writing request frequency is to be written in the writing buffer unit and the writing buffer unit is full, data stored in the writing buffer unit and having a relatively low using frequency may be stored in the flash memory, after which the data having the relatively high writing request frequency is stored in the writing buffer unit.

After the data having the relatively high writing request frequency is stored in the writing buffer unit, metadata may be updated.

According to still yet another aspect of the present invention, there is provided a data storage system including: a memory unit having a flash memory unit and a writing buffer unit; and a memory control unit including a page classification unit for classifying a writing request into one of a plurality of grades according to a writing request frequency when a writing request is made, wherein the memory control unit stores the writing requested data in one of the memory unit and the writing buffer unit according to the writing request frequency.

When the writing request is classified into one of two grades, the memory control unit may store data having a relatively high writing request frequency in the writing buffer unit and store data having a relatively low writing request frequency in the flash memory unit.

The writing buffer unit may include a plurality of writing buffers arranged in parallel.

Alternatively, when the writing request is classified into one of two grades, the memory control unit may temporarily store data having a relatively high writing request frequency in a first writing buffer of the plurality of writing buffers, temporarily store data having a relatively low writing request frequency in a second writing buffer of the plurality of writing buffers or in the flash memory unit.

Alternatively, when the writing request is classified into one of three grades, the memory control unit may temporarily store data having a relatively high writing request frequency in a first writing buffer of the plurality of writing buffers, temporarily store data having a middle writing request frequency in a second writing buffer of the plurality of writing buffers, and store data having a relatively low writing request frequency in the flash memory unit.

Alternatively, when the writing request is classified into one of three grades, the memory control unit may temporarily store data having a relatively high writing request frequency in a first writing buffer of the plurality of writing buffers, temporarily store data having a middle writing request frequency in a second writing buffer of the plurality of writing buffers, and temporarily store data having a relatively low writing request frequency in a third writing buffer of the plurality of writing buffers.

In the above-described systems and methods, the buffer may be one of a bank and a non-volatile memory chip having a predetermined data storage capacity. The first and second data storage devices may be first and second banks, respectively, and each of the first and second banks may include a plurality of pages each having a predetermined data storage capacity. The first and second data storage devices may be first and second flash memory chips, respectively.

The data storage capacity of the buffer may be equal to, or N (N=1, 2, 3) times, that of the page. The data storage capacity of the buffer may be equal to, or N (N=1, 2, 3) times, a block size that is a deleting unit of the flash memory.

The non-volatile memory unit and the flash memory unit may be formed in a single chip.

The storage unit may further include a flash translation layer and a second input/output bus functioning as an interface between the non-volatile memory buffer unit and the flash memory unit.

The storage unit may be provided in the form of a card that can be detachably installed on the host unit.

The host unit may further include a first file system, a second file system, a flash translation layer interfacing with the first file system, and a device driver interfacing with the second file system.

The non-volatile memory chip may be selected from the group consisting of an MRAM, a PRAM, an FRAM, a non-volatile polymer memory chip, and a combination thereof.

The writing buffer unit may be a battery attached type non-volatile memory.

The writing buffer unit may be a volatile memory.

The flash memory unit may include a NAND-type Single Level Cell (SLC) flash memory and a NAND-type Multi Level Cell (MLC) flash memory.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a block diagram of a data storage system having a complex memory according to an embodiment of the present invention;

FIG. 2 is a block diagram of a storage unit of FIG. 1 according to an embodiment of the present invention;

FIG. 3 is a block diagram of a data storage system with a complex memory according to another embodiment of the present invention;

FIG. 4 is a block diagram of a storage unit of FIG. 3 according to an embodiment of the present invention;

FIG. 5 is a block diagram illustrating a writing process in the data storage system of FIG. 1 or 3in reference to an applied clock cycle according to an embodiment of the present invention;

FIG. 6 is a block diagram illustrating a reading process in the data storage system of FIG. 1 or 3 in reference to an applied clock cycle according to an embodiment of the present invention;

FIG. 7 is a block diagram illustrating a data storage system with a complex memory according to another embodiment of the present invention; and

FIG. 8 is a flowchart illustrating a data storage method of the data storage system of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

FIG. 1 is a block diagram of a data storage system (hereinafter, referred as “first system”) having a complex memory according to an embodiment of the present invention.

Referring to FIG. 1, the first system includes a host unit 40, a storage unit 44 and a first I/O (input/output) bus 42. The first I/O bus 42 functions as an interface between the host unit 40 and the storage unit 44. The host unit 40 is a computer main body in which a file system 40 a is equipped. The storage unit 44 includes a flash translation layer 44 a, a non-volatile buffer unit 44 b, a second I/O bus 44 c, and a flash memory unit 44 d. The flash translation layer 44 a is provided in the form of hardware, which can identify data and a location where the data is recorded in the flash memory 44 d, perform the erasing operation, and identify data and a location where the data is recorded in the non-volatile memory buffer unit 44 b. Accordingly, the data recorded in the flash memory buffer unit 44 b can be read using the flash translation layer 44 a. The second I/O bus 44 c functions as an interface between the non-volatile memory buffer unit 44 b and the flash memory unit 44 d. The storage unit 44 is portable and can be detachably attached on the host unit 40. For example, the storage unit 44 may be any one of a compact flash card, a smart media card, a multimedia card, a secure digital card, a memory stick card, and a Universal Serial Bus (USB) storage device.

FIG. 2 is a block diagram of a storage unit of FIG. 1 according to an embodiment of the present invention. Referring to FIG. 2, the non-volatile memory buffer unit 44 b includes first through nth non-volatile memory buffers (hereinafter, referred as “buffers”) 44 b 1, 44 b 2 . . . 44 b(n-1), 44 b(n). The first through nth buffers 44 b 1,44 b 2 . . . 44 b(n-1), and 44 b(n) are connected in parallel. The first through nth buffers 44 b 1, 44 b 2 . . . 44 b(n-1), and 44 b(n) may be banks or chips each having a predetermined capacity. The banks or chips are MRAMs, FRAMs, PRAMs or non-volatile polymer memories. The flash memory unit 44 d may include first through mth banks 44 d 1, 44 d 2 . . . 44 d(m-1), and 44 d(m). Each of the first through mth banks 44 d 1, 44 d 2 . . . 44 d(m-1), and 44 b(m) includes a plurality of pages p1. Each page p1 has a predetermined capacity, which is preferably the same as that of each of the first through nth buffers 44 b 1, 44 b 2 . . . 44 b(n-1), 44 b(n) of the non-volatile memory buffer unit 44 b. That is, a capacity of one of the buffers forming the non-volatile memory buffer unit 44 b is identical to that of one of the pages p1 forming each of the first to mth banks 44 d 1, 44 d 2 . . . 44 d(m-1), and 44 d(m). For example, when the capacity of each buffer of the non-volatile memory buffer unit 44 b is 512 bytes, the capacity of one page p1 which forms each of the first through mth banks 44 d 1, 44 d 2 . . . 44 d(m-1), and 44 d(m) is also 512 bytes. Each of the first to mth banks 44 d 1, 44 d 2 . . . 44 d(m-1), and 44 d(m) may be formed using individual flash memory chips. The flash memory unit 44 d may include a NAND-type Single Level Cell (SLC) flash memory and a NAND-type Multi Level Cell (MLC) flash memory. At this point, each of the flash memories includes a plurality of banks that are connected in parallel.

Although it is preferable that the capacity of each buffer of the non-volatile memory buffer unit 44 b is same as that of each page p1 of the banks of the flash memory unit 44 d, the capacity of the buffer may be n (where n=1, 2, 3) times larger or smaller than the capacity of the page. Alternatively, the capacity of the buffer may be identical to or n times (n=1, 2, 3) the size of the block that is an erasing unit of the flash memory.

Meanwhile, in the nth buffer 44 b(n), the number “n” of the buffers (or banks) contained in the non-volatile memory buffer unit 44 b may be 2p+1 where the p represents a degree of the parallelism of the flash memory devices of the flash memory unit 44 d. The degree of the parallelism is a natural number that is identical to or less than a value obtained by dividing the writing speed of a flash memory device by the writing speed of a non-volatile memory device. For example, when the first through nth buffers 44 b 1, 44 b 2 . . . 44 b(n-1), 44 b(n) are FRAM devices and the first through mth banks 44 d 1, 44 d 2 . . . 44 d(m-1), and 44 d(m) of the flash memory unit 44 d are NAND-type flash memory devices, the writing speed of the FRAM devices is 100 ns/word and the writing speed of the NAND-type flash memory devices is 500 ns/word. Therefore, the degree “p” of the parallelism of the flash memory devices of the flash memory unit 44 d in relation to the FRAM devices is 5. In this case, the non-volatile memory buffer unit 44 b includes 11(2×5+1) buffers (or banks) and the flash memory unit 44 d includes 5 logical I/O banks.

FIG. 3 is a block diagram of a data storage system (hereinafter, referred to as “second system” ) having a parallel I/O complex memory according to another embodiment of the present invention.

Referring to FIG. 3, the second system D includes a host unit 50, a storage unit 54 and an I/O bus 52. The host unit 50, I/O bus 52 and storage unit 54 are equipped in a single main body. That is, while the storage unit 44 of the first system is a portable device such as a diskette that can be detachably attached to the host unit 40, the storage unit 54 and the host unit 50 of the second system may be chips that are mounted on a single board. The host unit 50 includes a file system 50 a and an additional file system 50 b. The host unit 50 further includes a flash translation layer 50 c associated with the operation of the file system 50 a and a device driver 50 d associated with the operation of the additional file system 50 b. The device driver 50 d is provided in the form of software. In the second system D, the I/O bus 52 functions as an interface between the host unit 50 and the storage unit 54. The storage unit 54 includes a non-volatile memory unit 54 a and a flash memory unit 54 b. The flash memory unit 54 b may include a NAND-type SLC flash memory and a NAND-type MLC flash memory.

FIG. 4 is a diagram showing the storage unit 54 of the second system D of FIG. 3 in more detail according to an embodiment of the present invention.

Referring to FIG. 4, the non-volatile memory buffer unit 54 a includes first through nth non-volatile memory buffers (hereinafter, referred as “buffers”) 54 a 1, 54 a 2 . . . 54 a(n-1), 54 a(n). The flash memory unit 54 b may include first through mth banks 54 b 1, 54 b 2 . . . 54 b(m-1), and 54b(m). The buffers 54 a 1, 54 a 2 . . . 54 a(n-1), 54 a(n) are arranged in parallel and the banks 54 b 1, 54 b 2 . . . 54 b(m-1), and 54 b(m) are also arranged in parallel. The parallel arrangements of the buffers and banks means that their structures are parallel and the operations thereof are performed in parallel. In this way, data can be recorded in the buffers and banks in parallel. The buffers 54 a 1, 54 a 2 . . . 54 a(n-1), 54 a(n) may be identical to those of the first system. Each of the banks 54 b 1, 54 b 2 . . . 54 b(m-1), and 54 b(m) includes a plurality of pages p2. Therefore, the banks 54 b 1, 54 b 2 . . . 54 b(m-1), and 54 b(m) may be identical to those of the first system. The banks 54 b 1, 54 b 2 . . . 54 b(m-1), and 54 b(m) may be formed using a single chip. Alternatively, each of the banks 54 b 1, 54 b 2 . . . 54 b(m-1), and 54 b(m) may be formed using individual flash memory chips.

Meanwhile, each of the flash memory units 44 d and 54 d of the first and second systems includes a NAND-type flash memory or a NOR-type flash memory. When the NOR-type flash memory is applied, data is input or output in units of bytes or words. In this case, it is difficult to manage the data.

Therefore, in the present invention, even when the flash memory is the NOR-type, the pages of the banks of each of the flash memory units 44 d and 54 d may be logical pages conceptually identical to the case when the flash memory is the NAND-type. In addition, when the NOR-type flash memory is applied to the flash memory units 44 d and 54 b, the size of each page of the banks may be identical to or different from that of the page of the banks when the NAND-type flash memory is applied.

When the NOR-type flash memory is applied and the pages of the banks are identical to that of the banks when the NAND-type flash memory is applied, the operation of the flash memory units 44 d and 54 b is identical to that when the NAND-type flash memory is applied, as will be described later.

Writing processes of the first and second systems will now be described with reference to FIG. 5.

In FIG. 5, the arrow indicates a dataflow direction from the non-volatile memory buffer unit to the flash memory unit. That is, the data written in the non-volatile memory buffer unit is moved to the flash memory unit.

In FIGS. 5 and 6, it is assumed that one clock signal and two clock signals are utilized for the reading and writing operations, respectively, of the non-volatile memory and two clocks and four clocks are utilized for the reading and writing operations, respectively, of the flash memory. The reading/writing speeds depend on the types of the non-volatile memory and the flash memory. The relative ratio between the reading/writing performance of the non-volatile memory and the reading/writing performance of the flash memory becomes a design factor in determining the number of buffers of the non-volatile memory and the number of banks of the flash memory to be utilized.

In FIG. 5, an example is given for convenience showing that the non-volatile memory buffer unit includes first to third buffers 70, 74 and 76 that are arranged in parallel and the flash memory unit includes first and second banks 80 and 90. At this point, the first bank 80 includes first through fifth pages 80 a, 80 b, 80 c, 80 d, and 80 e. The second bank 90 includes first through fifth pages 90 a, 90 b, 90 c, 90 d, and 90 e. The first through third buffers 70, 74 and 76 may be some of the buffers contained in the non-volatile memory buffer units 44 b and 54 a as shown in FIGS. 2 and 4, respectively. The first and second banks 80 and 90 may be some of the banks contained in the flash memory units 44 d and 54 b as shown in FIGS. 2 and 4, respectively.

Referring to FIG. 5, data is recorded in the first buffer 70 of the non-volatile buffer unit at a first clock pulse 1. The recording of the data in the first buffer 70 is continued until a second clock pulse 2. After the recording of the data in the first buffer 70 is finished, the data recorded in the first buffer 70 starts being recorded in the first page 80 a of the first bank 80 at a third clock pulse 3. The process for recording the data recorded in the first buffer 70 in the first page 80 a of the first bank 80 is continued until a sixth clock pulse. The time spent in recording the data recorded in the first buffer 70 in the first page 80 a of the first bank 80 is two times that spent in recording the data in one of the buffers of the non-volatile memory buffer unit. Therefore, while the data recorded in the first buffer 70 is recorded in the first page 80 a of the first bank 80, further data cannot be recorded in the first buffer 70. Therefore, while the data recorded in the first buffer 70 is recorded in the first page 80 a of the first bank 80, further data input to the non-volatile memory buffer unit is consecutively recorded in the second and third buffers 74 and 76. The point of time when data is recorded in the second and third buffers 74 and 76 depends on whether the data input to the non-volatile buffer unit is continuous or discontinuous. For example, if there is no data input to the non-volatile memory buffer unit until the data recorded in the first buffer 70 moves completely to the first page 80 a of the first bank 80, the following data input to the non-volatile memory buffer unit can be recorded again in the first buffer 70. On the other hand, if data is continuously input, further input data is recorded in the second buffer 74 after initial data is first input to the first buffer 70. That is, the recording of data to the second buffer 74 starts at the third clock pulse 3 and ends at a fourth clock pulse 4. The recording of the data recorded in the first buffer 70 to the first page 80 a of the first bank 80 is continued at the fourth clock pulse 4 where the recording of the data to the second buffer 74 is completed. After recording of the data to the second buffer 74 is completed, the data recorded in the second buffer 74 starts being recorded in the first page 90 a of the second bank 90. A process for recording the data recorded in the second buffer 74 in the first page 90 a of the second bank 90 starts at the fifth clock pulse 5 and continues until an eighth clock pulse 8. A process for recording the data recorded in the first buffer 70 in the first page 80 a of the first bank 80 starts at the third clock pulse 3 and continues until the sixth clock pulse 6. Therefore, during the fifth and sixth clock pulses 5 and 6, recording of the data to the first and second buffers 70 and 74 cannot be done. Recording of the data to the second buffer 74 cannot be done until the eighth clock pulse 8. Therefore, after the data is recorded in the second buffer 74, data input to the non-volatile memory buffer is recorded in the third buffer 76 at the fifth clock pulse 5. Recording of the data in the third buffer 76 continues until the sixth clock pulse 6. At the sixth clock pulse 6, the recording of the data to the third buffer 76 is completed and the data recorded in the first buffer 70 is recorded in the first page 80 a of the first bank 80. However, the data recorded to the second buffer 74 is continuously recorded in the first page 90 a of the second bank 90. As described above, at the sixth clock pulse 6 the recording of data to the third buffer 76 is completed and the first buffer 70 of the non-volatile memory buffer unit is empty. Therefore, further data being input to the non-volatile memory buffer unit at the seventh clock pulse 7 can be recorded to the first buffer 70.

The reading operation of the first or second system will now be described.

The reading operation of the first or second system is similar to a conventional data cashing method. That is, an address region that is frequently used is maintained in a part of the non-volatile RAM using the hardware cash or the LRU (Least Recently Used) software. When there is a reading request for the data remained in the non-volatile RAM, the data is quickly read from the non-volatile RAM without using the flash memory and transmitted. According to a feature of the present invention, a prefetching method is additionally utilized for the reading operation. In this case, the stored data is quickly read from the selected bank of the flash memory using the parallel structure and the prefetching of the data is done from the selected buffer of the non-volatile memory buffer unit.

In the above-described reading method, as in the writing operation, using the degree of the parallelism corresponding to the relative ratio of the reading performance between of the non-volatile RAM and the flash memory utilized, data that is expected to be read is first loaded on the selected buffer of the non-volatile memory buffer unit and data that is already read is pushed out.

When the estimation of data that is expected to be read is accurate, the reading speed may be identical to a case where data is read from the non-volatile RAM even when a buffer having a relatively small capacity is used.

FIG. 6 shows the reading process of the first or second system in reference to an applied clock cycle. In FIG. 6, the arrow indicates a dataflow direction.

Referring to FIG. 6, data recorded in the first page 80 a of the first bank 80 of the flash memory unit is read and recorded in the first buffer 70 of the non-volatile memory buffer unit (hereinafter, “first recording”). At this point, the bank 80 may be one of the banks contained in the SLC flash memory of the flash memory unit or one of the banks contained in the MLC flash memory of the f, In₂O₃, MoO₃ and a complex oxide thereof. Further, a perchlorate may be added to the elastomer material to impart conductivity.

In embodiments, a covering layer can also be provided on a surface of the contact charging unit. Materials for forming this covering layer may include N-alkoxymethylated nylon, a cellulose resin, a vinylpyridine resin, a phenol resin, a polyurethane, polyvinyl butyral and melamine, and these may be used either alone or as a combination of two or more of them. Furthermore, an emulsion resin material such as an acrylic resin emulsion, a polyester resin emulsion or a polyurethane, particularly an emulsion resin synthesized by soap-free emulsion polymerization can also be used. In order to further adjust resistivity, conductive agent particles may be dispersed in these resins, and in order to prevent deterioration, an antioxidant can also be added thereto. Further, in order to improve film forming properties in forming the covering layer, a leveling agent or a surfactant can also be added to the emulsion resin.

In embodiments, the resistance of the contact charging unit is from 10⁰ to 10¹⁴ Ωcm, or from 10² to 10¹² Ωcm. When a voltage is applied to this contact charging unit, either a DC voltage or an AC voltage can be used as the applied voltage. Further, a superimposed voltage of a DC voltage and an AC voltage can also be used. Such a contact charging unit may be in the shape of a blade, a belt, a brush or the like.

In embodiments, the exposure unit can be an optical device which can perform desired image wise exposure to a surface of the electrophotographic imaging member with a light source such as a semiconductor laser, an LED (light emitting diode) or a liquid crystal shutter. In various embodiments, the use of the exposure unit makes it possible to perform exposure to noninterference light.

In embodiments, the developing unit can be a known or later used developing unit using a normal or reversal developing agent of a one-component system, a two-component system or the like. There is no particular limitation on the shape of a toner used, and for example, an irregularly shaped toner obtained by pulverization or a spherical toner obtained chemical polymerization is suitably used.

In embodiments, the transfer unit can be a contact type transfer charging device using a belt, a roller, a film, a rubber blade or the like, or a scorotron transfer charger or a corotron transfer charger utilizing corona discharge.

In embodiments, the cleaning unit can be a device for removing a remaining toner adhered to the surface of the electrophotographic imaging member after a transfer step, and the cleaned electrophotographic imaging member is repeatedly subjected to the above-mentioned image formation process. The cleaning unit can be a cleaning blade, a cleaning brush, a cleaning roll or the like. In embodiments, a cleaning blade is used. Materials for the cleaning blade may include urethane rubber, neoprene rubber and silicone rubber.

In embodiments, an intermediate transfer belt is supported with a driving roll, a backup roll and a tension roll at a specified tension, and rotatable by the rotation of these rolls without the occurrence of deflection. Further, a secondary transfer roll can be arranged so that it is brought into abutting contact with the backup roll through the intermediate transfer belt. The intermediate transfer belt which has passed between the backup roll and the secondary transfer roll can be cleaned up by a cleaning blade, and then repeatedly subjected to the subsequent image formation process.

The disclosure should not be construed as being limited to the above-mentioned embodiments. For example, in embodiments, the image forming apparatus can be equipped with a process cartridge comprising the electrophotographic imaging member(s) and charging device(s). The use of such a process cartridge allows maintenance to be performed more simply and easily.

Furthermore, in embodiments, a toner image formed on the surface of the electrophotographic imaging member can be directly transferred to the medium. In various other embodiments, the image forming apparatus may be provided with an intermediate transfer body. This makes it possible to transfer the toner image from the intermediate transfer body to the medium after the toner image on the surface of the electrophotographic imaging member has been transferred to the intermediate transfer body. In embodiments, the intermediate transfer body can have a structure in which an elastic layer containing a rubber, an elastomer, a resin or the like and at least one covering layer are laminated on a conductive support.

In addition, in embodiments, the disclosed image forming apparatus may be further equipped with a static eliminator such as an erase light irradiation device. This prevents the incorporation of the residual potential of the electrophotographic imaging member into the subsequent cycle, when the electrophotographic imaging member is repeatedly used.

Examples are set forth below and are illustrative embodiments. It will be apparent to one skilled in the art that the embodiments can be practiced with many types of compositions and can have many different uses in accordance with the disclosure above and as pointed out hereinafter.

EXAMPLES

Undercoat layer containing cyanoresin polymer

In Comparative Example 1, the 3-component undercoat layer was prepared as following: zirconium acetylacetonate tributoxide (about 35.5 parts), γ-aminopropyltriethoxysilane (about 4.8 parts) and poly (vinyl butyral) (about 2.5 parts) were dissolved in n-butanol (about 52.2 parts) to prepare a coating solution. The coating solution was coated via a ring coater, and the layer was pre-heated at about 59° C. for about 13 minutes, humidified at about 58° C. (dew point of 54° C.) for about 17 minutes, and then dried at about 135° C. for about 8 minutes. The thickness of the undercoat layer on each photoreceptor was approximately 1.3 μm. The HOGaPc photogeneration layer dispersion were prepared as following: 2.5 grams of HOGaPc Type V pigment was mixed with about 1.67 grams of poly(vinyl chloride/vinyl acetate) copolymer (VMCH from Dow Chemical) and 30 grams of n-butyl acetate. The mixture was milled in an Attritor mill with about 130 grams of 1 mm Hi-Bea borosilicate glass beads for about 1.5 hours. The dispersion was filtered through a 20-μm nylon cloth filter, and the solid content of the dispersion was diluted to about 5 weight percent with n-butyl acetate. The HOGaPc photogeneration layer dispersion was applied on top of the 3-component undercoat layer. The thickness of the photogeneration layer was approximately 0.2 μm. Subsequently, an 32 μm charge transport layer (CTL), also called Brown II CTL, was coated on top of the photogeneration layer from a solution of N,N′-diphenyl-N,N-bis(3-methyl phenyl)-1,1′-biphenyl-4,4′-diamine (about 9.9 grams) and a polycarbonate, PCZ-400 [poly(4,4′-dihydroxy-diphenyl-1-1-cyclohexane, Mw=40000)]available from Mitsubishi Gas Chemical Co., Ltd. (about 12.1 grams), in a mixture of about 55 grams of tetrahydrofuran (THF) and about 23.5 grams of monochlorobenzene. The charge transport layer was dried at about 135° C. for about 45 minutes.

Cyanoethyl poly(vinyl alcohol) was produced by the reaction of acrylonitrile and poly(vinyl alcohol). An undercoat layer was prepared by dissolving this cyanoethyl poly(vinyl alcohol) (CR-V, Shin-Etsu Chemical Co., Ltd., Tokyo, Japan) in a DMF/methanol solvent (weight/weight ratio=40/60) with a solid content of approximately 5 weight %. The undercoat layer was coated onto a mirror aluminum substrate with a Tsukiage coater. In Example 1, the undercoat layer was coated at a thickness of 1.0 μm. In Example 2, the undercoat layer was prepared at a thickness of 2.0 μm. The undercoat layers were then dried at 160° C. for 15 minutes. In each of Examples 1 and 2, a photoreceptor was formed in the same manner as for Comparative Example 1 by replacing the 3-component UCL with the cyanoresin UCL.

The above prepared photoreceptor devices were tested in a scanner set to obtain photo induced discharge cycles, sequenced at one charge-erase cycle followed by one charge-expose-erase cycle, wherein the light intensity was incrementally increased with cycling to produce a series of photo induced discharge characteristic curves (PIDC) from which the photosensitivity and surface potentials at various exposure intensities were measured. Additional electrical characteristics were obtained by a series of charge-erase cycles with incrementing surface potential to generate several voltages versus charge density curves. The scanner was equipped with a scorotron set to a constant voltage charging at various surface potentials. The devices were tested at surface potentials of about 500 and about 700 volts with the exposure light intensity incrementally increased by means of regulating a series of neutral density filters; the exposure light source was a 780-nanometer light emitting diode. The aluminum drum was rotated at a speed of about 55 revolutions per minute to produce a surface speed of about 277 millimeters per second or a cycle time of about 1.09 seconds. The xerographic simulation was completed in an environmentally controlled light tight chamber at ambient conditions (about 40 percent relative humidity and about 22° C.).

The slopes of the PIDC curves (sensitivity) for the photoreceptors of Examples 1 and 2 did not significantly vary from the slope of the PIDC curve of the photoreceptors of Comparative Example 1. Accordingly, the sensitivities of the photoreceptors of Examples 1 and 2 are not adversely affected by the presence of cyanoresin polymers.

As illustrated in FIG. 2, the charge electric properties and the erase electric properties of the photoreceptors of Examples 1 and 2 did not significantly vary from the charge electric properties and the erase electric properties of the photoreceptor of Comparative Example 1. Accordingly, the electric properties of the photoreceptors of Examples 1 and 2 are not adversely affected by the presence of cyanoresin polymers.

Interface Layer containing Cyanoresin Polymer

In Comparative Example 2, a photoreceptor was formed by coating a TiSi undercoat layer onto a mirror aluminum substrate, coating a HOGaPc/VMCH charge generation layer onto the undercoat layer, and coating a 25-μm Brown II charge transport layer onto the charge generation layer. The TiSi undercoat layer was prepared as following: a titanium oxide/phenolic resin dispersion was prepared by ball milling 15 grams of titanium dioxide (STR-60N™, Sakai Company), 20 grams of the phenolic resin (VARCUM™ 29159, OxyChem Company, M_(w) of about 3,600, viscosity of about 200 cps) in 7.5 grams of 1-butanol and 7.5 grams of xylene with 120 grams of 1 millimeter diameter sized ZrO₂ beads for 5 days. Separately, a slurry of SiO₂ and a phenolic resin were prepared by adding 10 grams of SiO₂ (P100, Esprit) and 3 grams of the above phenolic resin into 19.5 grams of 1-butanol and 19.5 grams of xylene. The resulting titanium dioxide dispersion was filtered with a 20 micrometers pore size nylon cloth, and then the filtrate was measured with Horiba Capa 700 Particle Size Analyzer, and there was obtained a median TiO₂ particle size of 50 nanometers in diameter and a TiO₂ particle surface area of 30 m²/gram with reference to the above TiO₂/VARCUM™ dispersion. Additional solvents of 5 grams of 1-butanol, and 5 grams of xylene; 5.4 grams of the above prepared SiO₂/VARCUM™ slurry were added to 50 grams of the above resulting titanium dioxide/VARCUM™ dispersion, referred to as the coating dispersion. Then an aluminum drum, cleaned with detergent and rinsed with deionized water, was dip coated with the above generated coating dispersion at a pull rate of 160 millimeters/minute, and subsequently, dried at 145° C. for 45 minutes, which resulted in an undercoat layer (UCL) deposited on the aluminum and comprised of TiO₂/SiO₂/VARCUM™ with a weight ratio of about 60/10/40 and a thickness of 4 microns. The charge generation layer and transport layer were prepared as in Comparative Example 1.

Cyanoethyl poly(vinyl alcohol) was produced by the reaction of acrylonitrile and poly(vinyl alcohol). An interface layer was prepared by dissolving this cyanoethyl poly(vinyl alcohol) (CR-V, Shin-Etsu Chemical Co., Ltd., Tokyo, Japan) in a DMF/methanol solvent (weight/weight ratio=50/50) with a solid content of approximately 5 weight %. In Example 3, a photoreceptor was formed by coating a TiSi undercoat layer onto a mirror aluminum substrate. The interface layer was coated onto the undercoat with a Tsukiage coater, and dried at 120° C. for 15 minutes, providing an undercoat layer having a thickness of about 0.5 μm. A photoreceptor was formed in the same manner as for Comparative Example 2.

The above devices were electrically-tested with an electrical scanner set to obtain PIDCs, as described above for Examples 1 and 2 and Comparative Example 1.

The slope of the PIDC curve for the photoreceptor of Example 3 did not significantly vary from the slope of the PIDC curve of the photoreceptor of Comparative Example 2. Accordingly, the sensitivity of the photoreceptor of Example 3 is not adversely affected by the presence of cyanoresin polymers.

As illustrated in FIG. 3, the charge electric properties and the erase electric properties of the photoreceptor of Example 3 did not significantly vary from the charge electric properties and the erase electric properties of the photoreceptor of Comparative Example 2. Accordingly, the electric properties of the photoreceptor of Example 3 are not adversely affected by the presence of cyanoresin polymers.

It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, various presently unforesee acrylonitrile and poly(vinyl alcohol). An interface layer was prepared by dissolving this cyanoethyl poly(vinyl alcohol) (CR-V, Shin-Etsu Chemical Co., Ltd., Tokyo, Japan) in a DMF/methanol solvent (weight/weight ratio=50/50) with a solid content of approximately 5 weight %. In Example 3, a photoreceptor was formed by coating a TiSi undercoat layer onto a mirror aluminum substrate. The interface layer was coated onto the undercoat with a Tsukiage coater, and dried at 120° C. for 15 minutes, providing an undercoat layer having a thickness of about 0.5 μm. A photoreceptor was formed in the same manner as for Comparative Example 2.

The above devices were electrically-tested with an electrical scanner set to obtain PIDCs, as described above for Examples 1 and 2 and Comparative Example 1.

The slope of the PIDC curve for the photoreceptor of Example 3 did not significantly vary from the slope of the PIDC curve of the photoreceptor of Comparative Example 2. Accordingly, the sensitivity of the photoreceptor of Example 3 is not adversely affected by the presence of cyanoresin polymers.

As illustrated in FIG. 3, the charge electric properties and the erase electric properties of the photoreceptor of Example 3 did not significantly vary from the charge electric properties and the erase electric properties of the photoreceptor of Comparative Example 2. Accordingly, the electric properties of the photoreceptor of Example 3 are not adversely affected by the presence of cyanoresin polymers.

It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. 

1. A cyanoresin polymer, comprising a reaction product of a hydroxyl-containing polymer and acrylonitrile, wherein at least one side chain group of the cyanoresin polymer is a cyano group.
 2. The cyanoresin polymer of claim 1, wherein every side chain group of the cyanoresin polymer is a cyano group.
 3. The cyanoresin polymer of claim 1, wherein a dielectric constant of the cyanoresin polymer is greater than 5 at 20° C. and 1 kHz.
 4. The cyanoresin polymer of claim 1, wherein a dielectric constant of the cyanoresin polymer is 5-24 at 20° C. and 1 kHz.
 5. The cyanoresin polymer of claim 2, wherein a dielectric constant of the cyanoresin polymer is greater than 10 at 20° C. and 1 kHz.
 6. A cyanoresin, comprising one or more cyanoresin polymers of claim
 1. 7. An electrophotographic imaging member binder, comprising the cyanoresin polymer of claim
 1. 8. An electrophotographic imaging member binder, consisting of the cyanoresin polymer of claim
 1. 9. An electrophotographic imaging member, comprising: a support layer, a charge generation layer, a charge transport layer, an undercoat layer, comprising an undercoat binder, and optionally an interface layer, comprising an interface binder, wherein at least one of the undercoat binder and the interface binder comprises a cyanoresin polymer comprising a reaction product of a hydroxyl-containing polymer and acrylonitrile, wherein at least one side chain group of the cyanoresin polymer is a cyano group.
 10. The electrophotographic imaging member of claim 9, wherein the undercoat binder comprises the cyanoresin polymer.
 11. The electrophotographic imaging member of claim 9, wherein every side chain group of the cyanoresin polymer is a cyano group.
 12. The electrophotographic imaging member of claim 10, wherein the undercoat binder consists of the cyanoresin polymer.
 13. The electrophotographic imaging member of claim 9, comprising an interface layer comprising an interface binder, wherein the interface binder comprises the cyanoresin polymer.
 14. The electrophotographic imaging member of claim 13, wherein the interface layer has thickness of less than about 1.0 μm.
 15. The electrophotographic imaging member of claim 13, comprising an interface layer comprising an interface binder, wherein the interface binder consists of the cyanoresin polymer.
 16. The electrophotographic imaging member of claim 13, wherein the interface layer and the undercoat layer each comprises the cyanoresin polymer.
 17. The electrophotographic imaging member of claim 9, wherein a dielectric constant of the cyanoresin polymer is greater than 5 at 20° C. and 1 kHz.
 18. The electrophotographic imaging member of claim 9, wherein a dielectric constant of the cyanoresin polymer is greater than 10 at 20° C. and 1 kHz.
 19. A process cartridge comprising the electrophotographic imaging member of claim 9 and at least one of a developing unit and a cleaning unit.
 20. An image forming apparatus comprising at least one charging unit, at least one exposing unit, at least one developing unit, a transfer unit, a cleaning unit, and the electrophotographic imaging member of claim
 9. 